Paul,
I would try a small cylindrical rotary file about half the hole dia. You
might
flatten it out enough to start a drill. If the threads are too buggered up to
save you could drill larger and install a helicoil. I suppose the next size bolt
(3/8) is an option but I would prefer using a helicoil.
Grant 50 3100
Hudson29@aol.com wrote:
> September in SoCal is often one of our two most miserable months, and I
> never count on doing outdoor daytime activities this time of year. This
> summer has been the most comfortable I can ever recall, and this weekend was
> no exception. The high was only 74 degrees F, and a cool Spring breeze sprung
> up to make an absolutely splendid day.
>
> Over this weekend I pitched into cleaning up the old 235 in preparation
> for painting and reassembly. Among the chores was chasing some of the threads
> in the castings with a tap. I like this kind of work. You really get a sense
> of progress as the surfaces come clean and the new treaded fasteners turn
> easily in their holes.
>
> Some of these hole were filled with broken bolts. My old drill set seemed
> fine for wood and plastic, but proved hopeless on these steel bolt remnants
> so a new set of Vermont American "Titanium" drill bits was purchased to
> replace the old ones that I suspect were made of something like silly putty.
> Several folks had recommended "Cobalt" drills, but the place I was shopping
> in sold these individually, not as a set, so I settled for the Titanium ones.
>
> These new drills worked a treat on the small 1/4" stuff, and when I came
> to the last hole, I thought I was home free. That last hole proved to be more
> than a match for me this Sunday, however. The hole is 5/16 course, one of the
> four large fasteners that hold the oil pan in place. The broken bolt is
> forward on the cam side. The motor is mounted on a stand, and is rotated
> belly up so the pan area is easy to get at.
>
> This particular bolt is broken off about 1/4" into the hole, and sheared
> so steeply that it is impossible to get a drill started. I have a center
> punch that had worked well with the other bolts but wouldn't touch this. I
> tried drilling in at an angle, but the drill just did not find a purchase.
> Someone else had tried drilling out the bolt in the past and had got mostly
> the cast iron that the bolt threaded into. The thing is a real buggered up
> mess and had been hidden by a dab of black silicone.
>
> Has anybody got any suggestions on what to do with it now? This is the
> last broken bolt in the motor, and when it's out we can move on to other
> things.
>
> Paul O'Neil, Hudson29@aol.com
> 1951 Chevrolet 3600 Pickup Project, See it at:
> The Poor Man's Advanced Design Tech Tips Page
> http://home.earthlink.net/~conntest47/
> Fullerton, California USA
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